This invention relates generally to methods for molding plastics. More specifically, this invention relates to a mandrel-dip method for molding plastic products containing enclosed loops.
PVC or other plastic parts molded using the mandrel-dip method have traditionally been unable to efficiently contain enclosed loops. In the traditional mandrel-dip method, a mold or mandrel is heated to 300-400 degrees fahrenheit and then dipped into room temperature plastic resin. The plastic is attracted to the heated mandrel, attaches to the mandrel, and cures with the heat. As the plastic resin cools around the mandrel, it attains the form of the mandrel or mold.
To produce loops in plastic molded parts, it has traditionally been necessary to use a mandrel or mold having an enclosed loop. The mandrel having the enclosed loop is heated then dipped into room temperature plastic resin, the resin surrounds the mandrel loop in accordance with the above-described procedure. A disadvantage of using this process to produce plastic parts having continuous enclosed plastic loops is that once the resin has coagulated around the mold and set, the mold cannot be separated directly from the resulting plastic part. In order to separate the plastic from the mold, it is necessary either to cut the plastic part or break or sever the enclosed mandrel loop.
The industry has been unable to use the mandrel-dip method of plastic molding to mold polyvinyl chloride (PVC) or other plastics into parts having enclosed loops without requiring the destruction of the mandrel, cutting of the plastic part, or breaking the enclosed mandrel loop. Destruction of the mandrel in order to remove the plastic part is time consuming and expensive because mandrels or molds are costly and meant to be re-used to make other plastic parts. Cutting the plastic part in order to remove it from the mold is disadvantageous for several reasons. Not only is it a tedious process, it also reduces the strength of the loop and thus the longevity of the overall part. Breaking the enclosed mandrel loop is undesirable because once the loop has been severed, the mandrel must either be repaired or replaced before it can be used to make another part.
Therefore, there is a need for an apparatus and method for molding PVC and other plastic parts having continuous enclosed loops using the mandrel-dip method in which the mandrel can be removed from the plastic part without destroying or damaging the mandrel or mold, cutting the plastic part, or breaking the enclosed mandrel loop.
The industry would also be benefitted by plastic parts having enclosed loops that offer increased strength and resiliency.